In the process of xerography, a light image of an original to be copied is typically recorded in the form of a latent electrostatic image upon a photosensitive or a photoconductive member with subsequent rendering of the latent image visible by the application of particulate thermoplastic material, commonly referred to as toner. The visual toner image can be either fixed directly upon the photosensitive member or the photoconductor member, or transferred from the member to another support, such as a sheet of plain paper, with subsequent affixing by, for example, the application of heat and pressure of the image thereto.
To affix or fuse toner material onto a support member like paper, by heat and pressure, it is usually necessary to elevate the temperature of the toner and simultaneously apply pressure sufficient to cause the constituents of the toner to become tacky and coalesce. In both the xerographic as well as the electrographic recording arts, the use of thermal energy for fixing toner images onto a support member is known.
One approach to the heat and pressure fusing of toner images onto a support has been to pass the support with the toner images thereon between a pair of pressure engaged roller members, at least one of which is internally heated. For example, the support may pass between a fuser roller and a pressure roller. During operation of a fusing system of this type, the support member to which the toner images are electrostatically adhered is moved through a nip formed between the rollers with the toner image contacting the fuser roll thereby to effect heating of the toner images within the nip.
The process of transferring charged toner particles from an image bearing member marking device, such as a photoconductor, to an image support substrate like a sheet of paper involves overcoming cohesive forces holding the toner particles to the image bearing member. The interface between the photoconductor surface and image support substrate may not in many instances be optimal, thus, problems may be caused in the transfer process when spaces or gaps exist between the developed image and the image support substrate. One aspect of the transfer process is focused on the application and maintenance of high intensity electrostatic fields in the transfer region for overcoming the cohesive forces acting on the toner particles as they rest on the photoconductive member. Control of these electrostatic fields and other forces is a factor to induce the physical detachment and transfer of the charged toner particles without scattering or smearing the developer material. Mechanical devices that force the image support substrate into contact with the image bearing surface have also been incorporated into transfer systems.
More specifically, the process of transferring charged toner particles from an image bearing member, such as a photoconductive member, to an image support substrate, such as the copy sheet, may be accomplished by overcoming adhesive forces holding the toner particles to the image bearing member. In general, transfer of developed toner images in electrostatographic applications has been accomplished via electrostatic induction using a corona generating device, wherein the image support substrate is placed in direct contact with the developed toner image on the photoconductive surface while the reverse side of the image support substrate is exposed to a corona discharge. This corona discharge generates ions having a polarity opposite that of the toner particles, thereby electrostatically attracting and transferring the toner particles from the photoreceptive member to the image support substrate.
In the electrostatic transfer of the toner powder image to the copy sheet, it is necessary for the copy sheet to be in uniform intimate contact with the toner powder image developed on the photoconductive surface. Unfortunately, the interface between the photoreceptive surface and the copy substrate is not always optimal. In particular, non-flat or uneven image support substrates, such as copy sheets that have been mishandled, left exposed to the environment or previously passed through a fixing operation, such as heat and/or pressure fusing, tend to promulgate imperfect contact with the photoreceptive surface of the photoconductor. Further, in the event the copy sheet is wrinkled, the sheet will not be in intimate contact with the photoconductive surface and spaces, or air gaps will materialize between the developed image on the photoconductive surface and the copy sheet. Problems may occur in the transfer process when spaces or gaps exist between the developed image and the copy substrate. There is a tendency for toner not to transfer across these gaps, causing variable transfer efficiency and, in the extreme, can create areas of low or no transfer resulting in a phenomenon known as image transfer deletion. Clearly, an image deletion is very undesirable in that useful information and indicia are not reproduced on the copy sheet.
As described herein, the typical process of transferring development materials in an electrostatographic system involves the physical detachment and transfer over of charged toner particles from an image bearing photoreceptive surface into attachment with an image support substrate via electrostatic force fields. Thus, an aspect of the transfer process is focused on the application and maintenance of high intensity electrostatic fields in the transfer region for overcoming the adhesive forces acting on the toner particles as they rest on the photoreceptive member. In addition, other forces, such as mechanical pressure or vibratory energy, have been used to support and enhance the transfer process. Careful control of these electrostatic fields and other forces can be required to induce the physical detachment and transfer over of the charged toner particles without scattering or smearing of the developer material.
With the advent of multicolor electrophotography, it is desirable to use an architecture which includes a plurality of image forming stations. One example of the plural image forming station architecture utilizes an image-on-image (101) system in which the photoreceptive member is recharged, reimaged and developed for each color separation. This charging, imaging, developing and recharging, reimaging and developing, all followed by transfer to paper, can be completed in a single revolution of the photoreceptor in so-called single pass machines, while multipass architectures form each color separation with a single charge, image and develop, with separate transfer operations for each color.
Mechanical devices, such as rollers, have been used to force the image support substrate into intimate and substantially uniform contact with the image bearing surface. For example, there can be selected an electrically biased transfer roll system in an attempt to minimize image deletions. In other electrophotographic printing machines, such as the color producing Xerox Corporation 1065 machine, the copy sheet is provided with a precisely controlled curvature as it enters the transfer station for providing enhanced contact pressure.
However, the interface between the image bearing surface and the print sheet is rarely uniform. Print sheets that have been mishandled, left exposed to the environment, or previously passed through a fixing operation, such as heat and/or pressure fusing, tend to be non-flat or uneven. An uneven print sheet makes uneven contact with the image bearing surface. In the event that the print sheet is wrinkled, the sheet will not be in continuous intimate contact with the image bearing surface. Wrinkles in the sheet cause spaces or air gaps to materialize between the developed toner powder image on the image bearing surface and the print sheet. When spaces or gaps exist between the developed image and the print sheet, various problems may result. For example, there is a tendency for toner not to transfer across the gaps, causing variable transfer efficiency and creating areas of low toner transfer or even no transfer; a phenomenon known as image transfer deletion.
Image transfer deletion is undesirable in that portions of the desired image may not be appropriately reproduced on the print sheet. The area of a transfer assist blade (TAB) that contacts the photoreceptor will, in most instances, pick up residual dirt and toner from the photoreceptor surface. The next job run, which processes print sheets having a dimension greater than 10 inches, will have the residual dirt on the transfer assist blade transferred to the back side of the print sheet, resulting in an unacceptable print quality defect. More importantly, continuous frictional contact between the blade and the photoreceptor may cause permanent damage to the photoreceptor.
In single pass color machines, it is desirable to cause as little disturbance to the photoreceptor as possible so that motion errors are not propagated along the belt to cause image quality and color separation registration problems. One area that has potential to cause such a disturbance is when a sheet is released from the guide after having been brought into contact with the photoreceptor for transfer of the developed image thereto. This disturbance, which is often referred to as trail edge flip, can cause image defects on the sheet due to the motion of the sheet during transfer caused by energy released due to the bending forces of the sheet. Particularly in machines which handle a large range of paper weights and sizes, it is difficult to have a sheet guide which can properly position any weight and size sheet while not causing the sheet to oscillate after having come in contact with the photoreceptor.
There is a need for transfer assist members that substantially avoid or minimize the disadvantages illustrated herein.
Also, there is a need for transfer assist members that are wear resistant and that can be used for extended time periods without being replaced.
There is also a need for toner developed images transfer assist members that permit the continuous contact between a photoconductor and the substrate to which the developed toner image is to be transferred, and an apparatus for enhancing contact between a copy sheet and a developed image positioned on a photoconductive member.
Yet another need resides in providing xerographic printing systems, inclusive of multi-color generating systems, where there is selected a transfer assist member that maintains sufficient constant pressure on the substrate to which a developed image is to be transferred, and to substantially eliminate air gaps between the sheet and the photoconductor in that the presence of air gaps can cause air breakdown in the transfer field.
Further, there is a need for transfer assist members that enable suitable and full contact of the developed toner image present on a photoconductor and a substrate to which the developed image is to be transferred.
Additionally, there is a need for transfer assist members that contain durable compositions that can be economically and efficiently manufactured, and where the amount of energy consumed is reduced.
Yet additionally there is a need for a multilayered transfer assist member that includes as one layer a check film on the side exposed to a dicorotron/corona, and which member possesses excellent resistance characteristics.
Also, there is a need for transfer assist members where the check film layer can be generated roll to roll by economically extrusion processing.
Further, there is a need for transfer assist members with a combination of excellent durability that exert sufficient constant pressure on a substrate and permit the substrate to fully contact the toner developed image on a photoconductor, which members provide mechanical pressure about 20 percent of its function and electrostatic pressure/tailoring about 80 percent of its function, and where complete transfer to a sheet of a developed image contained a photoconductor results, such as for example, about 90 to about 100 percent, from about 90 to about 98 percent, from about 95 to about 99 percent, and in embodiments about 100 percent of the toner image is transferred to the sheet or a substrate, and wherein blurred final images are minimized or avoided.
Moreover, there is a need for composite transfer assist blades that overcome or minimize the problems associated with a single component blade, as a single component blade in order to be flexible enough to prevent image damage does not provide enough contact force to the back of the sheet to enable complete image transfer giving rise to transfer deletions and color shift. When a thick enough blade is used, the stress on the single blade material is high.
Yet, there is another need for transfer assist members that include check films, and which members are useful in electrophotographic imaging apparatuses, including digital printing where the latent image is produced by a modulated laser beam, or ionographic printing where charge is deposited on a charge retentive surface in response to electronically generated or stored images.
These and other needs are achievable in embodiments with the transfer assist members and components thereof disclosed herein.